The present invention relates to strain gage measuring devices and more specifically to a temperature compensated strain gage for measuring elongations of elastomeric materials.
Bonded wire resistance strain gages are commonly used to measure stress and strain produced in material specimens under load. Such a device is taught by U.S. Pat. Nos. 2,815,424 and 3,433,060. Both patents teach transmitting strain to a point remote from the specimen under test by means of a mechanical transducer formed as an arcurately shaped strip of resilient material. The first mentioned patent teaches attachment by means of sharp points at each end of the transducers for penetrating the test specimen. The last mentioned patent teaches permanently installing the transducers to the material to be monitored. These features create a disadvantage in that penetration causes damage to the specimen under test, as well as becoming disconnected from the specimen when stress and strain is encountered. Permanent installation of the strain gage is costly as the elements can not be reused. It is well known that source of measurement error exists with changes of temperature if the specimen is encountered. This error is defined as zero error. As the system zero reference changes, false reading occurs indicating non-existent dynamic stress. U.S. Pat. Nos. 3,290,928 and 3,303,693 take this factor into account by compensating for this apparent strain. Both of the methods taught require considerable expense in both fabrication and installation.
Clearly reuseable transducers and strain gages and an inexpensive method for continually compensating for temperature changes would be readily acceptable by industry.